Grinding machines with wear compensator



Nov. 12, 1957 S. MESSERSCHMIDT GRINDING MACHINES WITH WEAR COMPENSATOR Filed June 17. 1952 United States Patent f GRINDING MACHINES WITH WEAR COMPENSATOR Sebastian Messerschmidt, Schweinfurt, Germany Application June 17, 1952, Serial No. 293,933 In Germany October 1, 1948 Public Law 619, August 23, 1954 Patent expires October 1, 19.68

3 Claims. (Cl. 51-165) This invention relates to an apparatus to be used in connection with an internal grinding machine for the purpose of measuring the workpieces when they have been ground and at the same time for automatically adjusting the machine to the extent to which the grinding disc or wheel has been worn. The main advantages thereof are that the operator is relieved of the difiicult task of measuring the workpieces after the grinding operation and of adjusting the feeding mechanism so as to compensate for the variation that has occurred owing to wear of the grinding disc. This task not only requires great technical ability and sensitivity on the part of the operator, but also entails a substantial expenditure of time.

-In the mass production of small parts of which the insides have to be ground, two methods of compensating the wear of the grinding disc or wheel have been in general use heretofore. Both methods have in common the fact that the feed is positively restricted. In one case the feed of the grinding disc is restricted by fixed abutments; in the other case the path of the grinding disc is controlled within fixed limits by means of a cam.

In the first method, each time the workpiece was changed the dimensional accuracy was checked; if there was any variation as a result of wear of the grinding disc, the feed mechanism of the grinding disc was adjusted. This method demands high technical ability and sensitivity on the part of the operator.

In the second method, after each grinding operation a truing diamond swings in and trues the grinding disc by the maximum amount of wear of the grinding disc. This method requires no particular intelligence on the part of the operator, but entails great expense because of the Wearing out of the grinding disc and the diamond.

The disadvantages of these methods are avoided by means of the invention.

Accordingly, it is an object of the present invention to provide an apparatus for use with an internal grinding machine which obviates these disadvantages.

Another object of the present invention resides in the provision of a separate measuring device for the workpieces which is connected with the internal grinding machine, and more particularly with the positioning and feed mechanism thereof, to bring about an automatic adjustment to compensate for the wear of the grinding disc or wheel.

Still another object of the present invention resides in the provision of an adjusting mechanism to compensate for the wear of the grinding disc or wheel which is simple in structure and operation, yet offers great reliability, especially for use in mass production, to maintain uniformity of the machined or ground work pieces.

The grinding of the workpieces is etlected in a known manner, the grinding wheel spindle being moved towards the workpiece and away again by means of a constantly running cam. The workpiece ground in this manner is 2,812,623 Patented Nov. 12, 1957 2 then measured on a measuring device connected to the feed-in spindle. If the measuring devivce registers a variation from the desired value, it brings about automatic adjustment of the grinding disc by the amount of the grinding disc wear.

One embodiment of the present invention is illustrated in the accompanying drawings. The invention however is not restricted to the embodiment illustrated. In these drawings, 7

Figure l is a view of the measuring device in frontal elevation, and

Figure 2 is a longitudinal section through the device.

A grinding disc 2 is driven by means of a hollow shaft 3 from a motor (not shown). The hollow shaft 3 is arranged in a slide 4. This slide 4 can be adjusted by means of hand-wheel 5, through the intermediary of a threaded spindle 6. By rotation of the hand-wheel 5, the threaded spindle 6 is screwed into or out of a nut 7. A pin 8 prevents rotation of the nut 7 but permits it to move relatively to the casing 1. One end of a lever 9 presses against the nut 7. This lever is mounted pivotally on the shaft 19. The other end of the lever 9 slides on the cam disc 11. This cam disc 11 is rigidly connected to a bevel wheel 12. The bevel wheel 12 and the cam disc 11 rotate together on a shaft 13. The shaft 13 is mounted in the casing 1. A second bevel wheel 14, rigidly mounted on the shaft 15, meshes with the bevel wheel 12. The shaft 15 is rotatably mounted in bearings 16 and 17 in the casing 1. When the shaft 15 rotates, the cam disc 11 is rotated through the intermediary of the pair of bevel wheels 12 and 14. This also bring about movement of the lever 9 sliding on the cam disc 11. The spring 18, pressing against the slide 4 at one end and against a plate 19 at the other end, causes the slide 5i to follow the movement of the lever 9 through the distance a. This known feed system causes the grinding disc to make always the same restricted feed movement.

If the grinding disc 2 did not wear, all the ground workpieces 20 would be uniformly accurate in their dimensions.

In order automatic-ally to compensate this wear of the grinding disc, the spindle 6, which is itself mounted at 50 in the slide 4, carries a hollow shaft 22 mounted on ball bearings 21. This hollow shaft has a toothed rim 23 meshing with a spur gear 24. The spur gear 24 is driven by a gear 51 rigidly connected to the shaft 15. The spindle 6 and the hollow shaft 22 can be coupled together by a selectively engageable coupling or clutch 25. For this purpose there is in the machine an electromagnet 52 by means of which the coupling 25 is engaged. When the coupling is engaged by means of the electromagnet 52, rotation of the shaft 15 causes the hollow shaft 22 and thereby also the spindle 6 to turn. The spindle 6 will turn as long as the coupling 25 is en gaged. Rotation of the spindle 6 in the non-rotatable nut '7 causes a change in theposition of the grinding wheel slide 4 relatively to the workpiece 2%). The coupling 25 can be engaged for exactly the right length of time to make the adjustment of the slide 4 correspond to the grinding disc wear. This is achieved by means of a measuring and adjusting device 25. The measuring de vice is positively connected to the grinding machine.

Two feeler fingers 27 and 28 receive the workpiece 20 that has just been ground. The feeler finger 28 is electrically insulated by means of an insulation 29. Also, the feeler finger 28 is'mounted to pivot about a shaft 30. The feeler finger 28 is provided with a connecting screw 31 for connecting the electric lead. The feeler finger 23 mounted on the shaft 36 is provided at its other end with a lever 32. This lever 32 impinges against an adjustable abutment 33 and a further abutment 34. This abutment 34 is mounted rotatably on ball bearings 35, of which the inner rings rest on the spindle 6. By means of a coupling 36, the abutment 34 can be rigidly connected to the spindle 6. Actuation of this coupling 36 also is effected by means of the electromagnet 52;. As soon as the coupling 36 is engaged, the abutment 34 rotates with the spindle 6. As soon as the current exciting the clectromagnet 52 ceases, the coupling 36 is released. When the coupling 36 is released a tension spring 37, hooked on to the pin 38 at one end and on to the abutment 34 at the other end, draws the abutment 34 back until the lever 32 is again held firmly in contact with the abutment 33. The pin 3% is of course rigid with the casing 1. The feeler finegr 27 is pivotally mounted on a shaft 39. The opposite end of this finger acts. through an adjusting screw 40, on an indicating device 41 accommodated in a casing 42. In the casing 42 there is a dropping loop id mounted to pivot about a pin 43. The dropping loop 44 is formed as a current conductor. The indicating device is provided with two rails 45 and 4 6. The indicating device ends in an indicator 47 which indicates the measured value on a scale 48. The measuring device may be so adjusted that when a mark 4% is reached the dropping loop 44 falls from the rail 46 on to the rail 45.

The following parts are electrically connected in series: the electromagnet 52, the feeler finger 28, the workpiece 20', the feeler finger 27, the rail 46 and the dropping loop 44. If the workpiece 21b is electrically non-conducting, it may be replaced by a separate switch for closing the circuit after the workpiece has been placed over the feeler fingers.

Automatic feed adjustment of the slide 4, corresponding to the grinding disc wear, is effected in the following manner:

When the apparatus is not in use, the indicator 47 is in its extreme right-hand position beyond the mark 49, and the dropping loop 44 rests on the rail 45. in order to place a freshly ground workpiece 2h round the feeler fingers 2'7 and 28, the finger 27 is lowered by raising its opposite end containing the adjustment screw M. This causes the indicator 47 to move to its extreme left-hand position. The workpiece 24) is then put in place and the opposite end of the finger 27 is released, so that the finger 27 rises. This movement is limited by the workpiece 2.0. The rising of the finger causes the indicator to leave its extreme left-hand position and move in the direction of the mark 4-) after having moved the dropping loop as off the rail 45 and on to the rail 46. Since normally the internal diameter of the ground workpiece is smaller than the desired value, the indicator S7 will not reach the mark 49. Therefore, as the dropping loop 44 rests on the conducting rail as the electric circuit is closed. The electromagnet 52, therefore, engages the coupling 25 and the coupling 36. This causes the spindle 6 to be displaced in the nut 7 in a clockwise direction and the grinding wheel to be adjusted. in order to limit the adjustment, during the movement of the spindle resulting from the engagement of the coupling 25 the abutment 34 also is connected with a shaft 6 by the coupling 36 and turns with the spindle. Therefore, the lever 32. moves away from the stationary abutment 33, since it follows the abutment 34 which is moving away, said lever being constantly urged towards the abutment 34 under the action of gravity or by means of a suitably arranged spring 34' or the like. This causes the feeler finger 2% to move upwards, whereby the feeler finger 27 may move in the same direct-ion, i. e., upwardly. This causes the indicator 47 to be deflected in the direction of the mark 49. As soon as the indicator 47 has reached the abutment 49, the dropping loop 44 falls off the rail 46. The current is thereby interrupted and the electromagnet 52 switched off. The couplings 25 and 36 are thereby disengaged. Th threaded spindle is immediately brought to a standstill by its own friction, while the spring 37 draws the abutment S t back. The lever 32., also, is thereby turned back towards the abutment 33. Thus, the feeler finger 28 again becomes a fixed measuring point. As normally the adjustment has been sufficient the workpiece 2%) is removed from the measuring device. The removal of the workpiece 29', causes the circuit to remain open until a new workpiece bridges over the contacts 27 and 28. if these workpieces 2t 2t) and so on are not used as contact bridges, for example, by reason of the nature of the non-conductive material thereof, then obviously a switch must be inserted for closing the circuit after the workpiece has been placed around the feeler fingers 27 and 28.

What I claim is:

l. A grinding machine comprising a casing, means in said grinding machine for grinding the work pieces, a feed adjusting mechanism for said last-mentioned means, a device on said casing having two feelers for receiving the work piece to be measured and being movable relatively to each other to contact the ground surfaces of said work piece, an electric circuit, a magnet connected in said circuit, an indicator connected to and operable by said feelers including a switching device connected in said electric circuit and adapted to interrupt said electric circuit in a certain position of said indicator, means including a coupling operated by said magnet for setting said feed adjustment mechanism into operation, and means coacting with said last-mentioned means to trans mit the movement of said feed adjusting mechanism to the said indicator and operative to adjust the firstmentioned means for grinding the work pieces when a finished work piece indicates wear of the grinding wheel.

2. An apparatus for compensating the grinding-disc wear in internal grinding machines comprising a feed adjustment mechanism, coupling means for selectively setting said feed adjustment mechanism into operation, and electromagnetic means for electrically engaging said coupling means to compensate for said wear, said lastnamed means including a separate measuring device for measuring the ground internal surfaces of the work pieces to detect any deviation from a predetermined dimension, an indicating device for visually indicating such deviation with energizing means responsive to such deviation for electrically energizing said electromagnetic means, and means operated upon engagement of said coupling means for disabling said energizing means upon sufficient movement by said feed adjustment mechanism to compensate exactly for said wear.

3. An apparatus for compensating the grinding-disc wear in internal grinding machines provided with a feed adjustment mechanism comprising measuring means provided with two measuring points and including an electric circuit adapted to be opened and closed, switch means for selectively closing said circuit upon emplacement of a ground work piece over said points, and an indicating device operatively connected with said points and provided with interrupting means for opening said circuit, lever means for transmitting the movement of said feed adjustment mechanism to said indicating device and for actuating said interrupting means, coupling means for selectively setting said feed adjustment mechanism and said lever means into operation, and an electromagnet energized by said circuit upon closure of said switch and interrupting means for engaging said coupling means to set said feed adjustment mechanism into operation to compensate for wear in the grinding disc and for automatically stopping said feed adjustment mechanism by de-energization of said electromagnet upon opening of said interrupter means by said lever means when said wear is exactly compensated for by said feed adjustment mechanism.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Mueller Aug. 11, 1925 Hutchinson Aug. 15, 1933 Nenninger Feb. 19, 1935 Greiner et a1. Mar. 5, 1940 6 Astrowski Dec. 23, 1941 Elberty Apr. 21, 1942 Jagen Nov. 1, 1949 FOREIGN PATENTS Germany May 23, 1955 France May 20, 1953 

